Project Summary/Abstract The goal of this proposal is to determine the potential of endogenous epithelial progenitor cells to contribute to regenerative approaches for emphysema therapies. Emphysema is a major phenotype of chronic obstructive lung disease (COPD) and affects over 4 million people in the US. It is characterized by progressive loss of alveolar lung tissue without therapies that stop or reverse the disease. Importantly, the endogenous ability of the distal lung to activate self-repair mechanisms is defective in emphysema, raising the question why and which regenerative pathways and/or cells are silenced in emphysema. WNT/beta-catenin signaling has been recently identified as a potential regenerative pathway with reduced activity in emphysema and re-activation of WNT/beta- catenin signaling has been shown to initiate intrinsic lung tissue repair. However, the mechanisms and the identity of potential progenitor cells that respond to WNT/?-catenin signaling and contribute to the repair of tissue destruction in chronic lung diseases, remain unknown. My preliminary studies using transgenic Wnt/beta-catenin activity reporter mice and a progenitor cell derived 3D lung organoid assay have identified a unique lung epithelial population which forms airway and alveolar organoids and exhibits high sensitivity to the modulations of WNT/beta-catenin signaling, thus representing a WNT/beta-catenin responsive progenitor population. Further, population and single cell transcriptome analysis has led to the identification of an airway club cell progenitor population as the major cell type in the WNT/beta-catenin responsive population. Thus, the aim of this proposal is to address the central hypothesis that WNT/beta-catenin signaling activates club cells to regenerate alveolar tissue in the emphysematous lung. This hypothesis will be tested in 3 Specific Aims: 1). Test the hypothesis that the club cell population is WNT/beta-catenin responsive and forms organoids; 2). Determine the fate and phenotype of the club cell population in murine emphysema models in vivo and their regenerative capacity upon WNT/beta-catenin activation; 3). Test the hypothesis that the club cell population respond to WNT/beta-catenin activation in human emphysematous lung tissue. The proposed work will solve an existing challenge by defining a precise WNT/beta-catenin-responsive club cell population in both mouse and human lungs and by identifying novel marker genes allowing to elucidate their alterations and regenerative potential in emphysema. This work and the integrated training plan will allow the investigator to establish comprehensive knowledge on lung injury and regeneration and expertise and skills to subsequently define the molecular mechanism leading to successful lung tissue regeneration in a future independent research career.